(1) Field of the Invention
The present invention relates to a method of processing spectacle frame shape data in a frame shape measuring apparatus for measuring shapes of spectacle frames, which method is applied before lenses are ground or cut in accordance with a frame shape to be fitted in the frame, and more particularly, to a spectacle frame shape data processing method capable of accurately measuring three-dimensional spectacle frame shapes, such as the distance between frame rims, inclination of the frame rims, and contour of an inner peripheral groove, and correcting the measured values such that the shapes of the frame rims are in bilateral symmetry.
(2) Description of the Related Art
The applicant hereof previously proposed a spectacle lens supply system (Japanese Patent Application No. 4-165912), wherein a desirable lens shape including a bevel figure is calculated at a lens processor side in accordance with information on lens, frame and prescription values transmitted from a lens orderer side, accept/reject information as to whether a lens process including a beveling is possible or not and also an estimated shape of a finished lens including a bevel figure are created based on the received information and supplied to the lens orderer side to be displayed on screen, and the lens orderer side determines whether the lens process including beveling is possible or not, based on the accept/reject information, or confirms the estimated shape of finished lens, to decide and order a lens with an optimum bevel based on the displayed information.
To accomplish such a system, first of all, the frame shape must be determined with accuracy. In particular, measurement values related to the frame shape must be processed with precision to obtain three-dimensional data.
Of the data representing a frame shape, the distance between the right and left frame rims and the inclination thereof are very important data when reproducing a three-dimensional image of spectacles in such a manner that the two frame rims are accurately positioned like real spectacles.
Thus, it is necessary that the distance between the frame rims and the inclination thereof be obtained by processing the measurement values related to the three-dimensional frame shape with precision.
In conventional methods, however, the measurement and the subsequent calculation are performed on condition that the forward direction of spectacles coincides with the Z axis of the frame shape measuring apparatus (vertical axis of a probe shown in FIG. 4). Accordingly, when mounting spectacles to the measuring apparatus, the forward direction of the spectacles must be aligned exactly with the Z axis of the measuring apparatus, thus requiring significant labor for the adjustment.
Furthermore, in practice, there inevitably occurs an error between the forward direction of the spectacles and the Z axis of the frame shape measuring apparatus, making it impossible to accurately calculate the distance between the frame rims and the inclination thereof.
The frame shape measuring apparatus acquires the contour of an inner peripheral groove cut in each frame rim based on the path of travel of a probe which moves along the inner peripheral groove in contact therewith and which has a symmetrical shape with respect to an axis of rotation symmetry. Specifically, the bottom contour of the inner peripheral groove is obtained by projecting the travel path of the center of the probe onto an XY plane and correcting individual points of the projected curve in respective normal directions by an amount equal to the radius of the probe.
However, while the axis of rotation symmetry of the probe is always parallel with the Z axis of the frame shape measuring apparatus, the contour of the inner peripheral groove of the frame rim varies not only in the X- and Y-axis directions but also in the Z-axis direction. Thus, in some cases, the probe may obliquely contact the inner peripheral groove which is V-shaped, possibly causing situations where the edge of the probe is displaced and separated from the bottom of the inner peripheral groove. The conventional correction method mentioned above is unable to cope with such awkward situations; namely, the bottom contour of the inner peripheral groove of the frame rim is erroneously calculated to be smaller than the actual contour by an amount corresponding to the displacement. This problem arises also when the angle of the edge of the probe is large.
As mentioned above, although the shape of a spectacle frame is measured under condition that the forward direction of the spectacles is in alignment with the Z axis of the frame shape measuring apparatus, the axis adjustment consumes much labor, and when the frame is actually mounted to the measuring apparatus, there often arises an error between the forward direction of the spectacles and the Z-axis direction of the measuring apparatus. Thus, even if the same frame is used, the error between the forward direction of the spectacles and the Z axis of the frame shape measuring apparatus, and thus the displacement of the edge of the probe, are subject to variation each time the frame is mounted to the measuring apparatus. As a result, a different contour is derived as the bottom contour of the inner peripheral groove of the frame rim each time the frame is mounted to the frame shape measuring apparatus, though the frame measured is the same. Particularly, the circumference of the inner peripheral groove obtained based on the bottom contour of the groove is greatly affected.
In order to further sophisticate the spectacle lens supply system, the right and left frame rims should be well balanced.
In general, the right and left frame rims should preferably have an identical shape from the viewpoint of outer appearance, but the frame rims sometimes develop a shape difference therebetween due to deformation which may be caused during shipment after manufacture, or by improper handling while being kept, or due to change with time attributable to the frame material. If lenses, for example, bifocal lenses each including a small lens piece, are fitted in a deformed frame, taking no notice of the deformation, the layout position of the small lens piece may differ between the right and left sides. The difference in layout position between the right and left small lens pieces gives rise to poor-balanced spectacles, which may give a strange feeling to a person in front of the spectacles wearer. To make the right and left frame rims well-balanced, a method has been proposed (e.g., in Examined Japanese Patent Publication (KOKOKU) No. 3-25298) in which both lenses are processed based on the shape of one of the right and left frame rims, and the other frame rim is deformed so as to be identical with the counterpart before the lenses are fitted in the frame.
In this conventional method, however, since the shape of one of the frame rims is left unchanged and is used as a reference shape, the other frame rim must be deformed by a large margin if there is a great shape difference between the actual right and left frame rims. Thus, this method is not desirable because application thereof is restricted by the deformation limit.
Further, if the right and left frame rims have different circumferences, a lens which has been processed according to the shape of one of the frame rims cannot be closely fitted in the other frame rim, though the frame rim is deformed by the conventional method.
Furthermore, even though the right and left frame rims have the same shape, they may be inclined differently with respect to the datum line of spectacles, In such cases, the inclination of the frame rim with respect to the datum line changes when the frame rim is deformed by the above method, with the result that the lens axes become misaligned when the lenses are fitted in the frame.
In the conventional method, moreover, since the right and left frame rims are visually checked for shape difference, the results of inspection differ from checker to checker and it is difficult to achieve accurate inspection with stability.